Brush tool stops working after changing tools

When I am using a tool in Photoshop, (mostly paintbrush tool) and then switch to zoom tool and then back to the brush tool, the brush tool stops working...there is no response for a time. Sometimes after trying multiple times it resumes working. What is going on and how can I fix this?
Thanks

Hi, Dave...Thanks for answering.
I am running MAC 10 Yosemite. and Creative Cloud Photoshop. I think it is automatically updated.
Yes I have a Wacom tablet, but I have never had this issue before getting Photoshop CC.
The Brush tool usually does work fine except sometimes as i have described above. It is not really a delay, it just stops responding. Sometimes after doing many many repeated scribble motions on my tablet, it will start working again...very mysterious, but also annoying.

Well, my first impulse would be that either your Wacom or some of the software that comes with it is stealing focus. It certainly wouldn't be the first time we've heard this, in fact. Not to throw them under the bus, but, well, you did notice that I immediately asked if you had a tablet connected...

To test my hunch, may I suggest unplugging the tablet AND completely removing ALL the software that came with it. I'd bet cash that the problem will go away. But, it'd nice to have you confirm it. 8-) Then, I can use that info and pass it along to Wacom.

The only other things I can come up with are that you've got another process stealing focus (unlikely, unless you've got a LOT of stuff running and you're also on a network with loads of requests) or (even less likely) there's another app stealing focus. Again, not at all likely, but well, I'm thorough...